<template>
  <el-color-picker
    v-model="theme"
    class="theme-picker"
    popper-class="theme-picker-dropdown"/>
</template>

<script>

const version = require('element-ui/package.json').version; // element-ui version from node_modules
const ORIGINAL_THEME = '#409EFF'; // default color

export default {
    data() {
        return {
            chalk: '', // content of theme-chalk css
            theme: ORIGINAL_THEME
        };
    },
    watch: {
        theme(val) {
            const oldVal = this.theme;
            if (typeof val !== 'string') return;
            const themeCluster = this.getThemeCluster(val.replace('#', ''));
            const originalCluster = this.getThemeCluster(oldVal.replace('#', ''));
            console.log(themeCluster, originalCluster);
            const getHandler = (variable, id) => {
                return () => {
                    const originalCluster = this.getThemeCluster(ORIGINAL_THEME.replace('#', ''));
                    const newStyle = this.updateStyle(this[variable], originalCluster, themeCluster);

                    let styleTag = document.getElementById(id);
                    if (!styleTag) {
                        styleTag = document.createElement('style');
                        styleTag.setAttribute('id', id);
                        document.head.appendChild(styleTag);
                    }
                    styleTag.innerText = newStyle;
                };
            };

            const chalkHandler = getHandler('chalk', 'chalk-style');

            if (!this.chalk) {
                const url = `https://unpkg.com/element-ui@${version}/lib/theme-chalk/index.css`;
                this.getCSSString(url, chalkHandler, 'chalk');
            } else {
                chalkHandler();
            }

            const styles = [].slice.call(document.querySelectorAll('style'))
                .filter(style => {
                    const text = style.innerText;
                    return new RegExp(oldVal, 'i').test(text) && !/Chalk Variables/.test(text);
                });
            styles.forEach(style => {
                const { innerText } = style;
                if (typeof innerText !== 'string') return;
                style.innerText = this.updateStyle(innerText, originalCluster, themeCluster);
            });
            this.$message({
                message: '换肤成功',
                type: 'success'
            });
        }
    },

    methods: {
        updateStyle(style, oldCluster, newCluster) {
            let newStyle = style;
            oldCluster.forEach((color, index) => {
                newStyle = newStyle.replace(new RegExp(color, 'ig'), newCluster[index]);
            });
            return newStyle;
        },

        getCSSString(url, callback, variable) {
            const xhr = new XMLHttpRequest();
            xhr.onreadystatechange = () => {
                if (xhr.readyState === 4 && xhr.status === 200) {
                    this[variable] = xhr.responseText.replace(/@font-face{[^}]+}/, '');
                    callback();
                }
            };
            xhr.open('GET', url);
            xhr.send();
        },

        getThemeCluster(theme) {
            const tintColor = (color, tint) => {
                let red = parseInt(color.slice(0, 2), 16);
                let green = parseInt(color.slice(2, 4), 16);
                let blue = parseInt(color.slice(4, 6), 16);

                if (tint === 0) { // when primary color is in its rgb space
                    return [red, green, blue].join(',');
                } else {
                    red += Math.round(tint * (255 - red));
                    green += Math.round(tint * (255 - green));
                    blue += Math.round(tint * (255 - blue));

                    red = red.toString(16);
                    green = green.toString(16);
                    blue = blue.toString(16);

                    return `#${red}${green}${blue}`;
                }
            };

            const shadeColor = (color, shade) => {
                let red = parseInt(color.slice(0, 2), 16);
                let green = parseInt(color.slice(2, 4), 16);
                let blue = parseInt(color.slice(4, 6), 16);

                red = Math.round((1 - shade) * red);
                green = Math.round((1 - shade) * green);
                blue = Math.round((1 - shade) * blue);

                red = red.toString(16);
                green = green.toString(16);
                blue = blue.toString(16);

                return `#${red}${green}${blue}`;
            };

            const clusters = [theme];
            for (let i = 0; i <= 9; i++) {
                clusters.push(tintColor(theme, Number((i / 10).toFixed(2))));
            }
            clusters.push(shadeColor(theme, 0.1));
            return clusters;
        }
    }
};
</script>

<style>
.theme-picker .el-color-picker__trigger {
  vertical-align: middle;
}

.theme-picker-dropdown .el-color-dropdown__link-btn {
  display: none;
}
</style>
